Methods for Generating and Applying Compression Within a Body

ABSTRACT

This disclosure describes exemplary screw and intramedullary devices that are better able to bring bone fragments into close proximity with each other, generate a compressive load, and maintain that compressive load for a prolonged period of time while healing occurs. The devices are made of a shape memory material.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.17/392,566, filed on Aug. 3, 2021; which is a continuation of U.S.patent application Ser. No. 16/416,930 filed on May 20, 2019, issued asU.S. Pat. No. 11,103,293 on Aug. 31, 2021; which is a divisionalapplication of U.S. patent application Ser. No. 15/288,131, filed onOct. 7, 2016, issued as U.S. Pat. No. 10,292,745 on May 21, 2019; whichclaims priority to U.S. Provisional Application No. 62/238,199 filed onOct. 7, 2015; and claims priority to U.S. Provisional Application No.62/238,210 filed on Oct. 7, 2015; and claims priority to U.S.Provisional Application No. 62/293,453, which was filed on Feb. 10,2016. The above-noted Applications are incorporated by reference as ifset forth fully herein.

TECHNICAL FIELD

This disclosure relates to devices and methods for generating, applying,and maintaining compression to a site in a human or animal body in orderto effect healing of diseased or damaged tissue. The disclosure findsparticular utility in the field of orthopedics and specifically forgenerating and maintaining compression between bone fragments that areto be fused. While the disclosure has application throughout the body,its utility will be described herein in the context of the repair ofinjured bone tissue, such as the proximal and distal interphalangealjoint of the second, third, or fourth toe and/or fingers. Additionally,the disclosure has application to aid in the fusion of broken ribs, etc.

BACKGROUND

In the field of orthopedic surgery, it is common to rejoin broken bones.The success of the surgical procedure often depends on the successfulreapproximation of the bone fragments, the amount of compressionachieved between the bone fragments, and the ability to maintain thatcompression between the bone fragments. If the surgeon is unable tobring the bone fragments into close contact, a gap will exist betweenthe bone fragments and the bone tissue will need to fill that gap beforecomplete healing can take place. Furthermore, gaps between bonefragments that are too large allow motion to occur between the bonefragments, disrupting the healing tissue and thus slowing the healingprocess. Optimal healing requires that the bone fragments be in closecontact with each other, and for a compressive load to be applied andmaintained between the bone fragments. Compressive strain between bonefragments has been found to accelerate the healing process in accordancewith Wolf s Law.

Broken bones can be rejoined using screws, staples, plates, pins,intramedullary devices, and other devices known in the art. Thesedevices are designed to assist the surgeon with reducing the fractureand creating a compressive load between the bone fragments.Intramedullary devices are often used for fractures of the long bones;however, they are also frequently used in the phalanges and specificallyfor the treatment of “hammer toe”, which is a deformity of the proximalinterphalangeal joint of the second, third, or fourth toe causing thetoe to be permanently bent. Typical intramedullary devices used in thephalanges have opposing ends that are adapted to grip against the wallof the intramedullary canal. These intramedullary devices are typicallymade of titanium alloys, stainless steel alloys, Nitinol and othermaterials, e.g., PEEK. The titanium alloy devices and stainless steelalloy devices often have barbs or threaded regions at their opposingends to grip the wall of the intramedullary canal. The Nitinol devicestypically have a pair of radially extending “legs” at their opposingends that expand outward when warmed to body temperature, with the pairof legs at each end being disposed in a common plane.

While these intramedullary devices are designed to bring the bonefragments into close contact and to generate a compressive load betweenthe bone fragments, these devices do not always succeed in accomplishingthis objective. The compressive load dissipates rapidly as the bonerelaxes and remodels. Furthermore, gripping the bone with only a pair ofcoplanar legs does not provide significant torsional stability to thefusion site.

Thus, there exists a clinical need for intramedullary devices that arebetter able to bring bone fragments into close proximity with eachother, generate a compressive load, and maintain that compressive loadfor a prolonged period of time while healing occurs.

SUMMARY

This disclosure contemplates the provision and use of a novel screw andintramedullary devices that are better able to bring bone fragments intoclose proximity with each other, generate compressive loads, andmaintain the compressive loads for a prolonged period of time whilehealing occurs.

In an exemplary embodiment, a compression screw is provided which ismanufactured from a shape memory material. The shape memory material maybe a metal alloy (e.g., Nitinol) or a polymer (e.g., appropriatelyprocessed PEEK). The compression screw is designed to engage bonefragments and to generate compression between the bone fragments. Thecompression screw has a proximal threaded region and a distal threadedregion. The thread pitch on the proximal threaded region is finer thanthe thread pitch on the distal threaded region (i.e., the thread pitchon the proximal threaded region has more threads per inch than thethread pitch on the distal threaded region). This pitch differentialaids in reducing fractures and generating compression between the bonefragments.

The thread geometry on the proximal threaded region and the distalthreaded region are mirrored to create a “book-end” effect thatincreases the compression holding capabilities of the screw (e.g., thethread geometry on the proximal threaded region has an incline in theproximal direction and a flat surface in the distal direction that issubstantially perpendicular to the longitudinal axis of the screw, andthe thread geometry on the distal threaded region is mirrored, having anincline in the distal direction and a flat surface in the proximaldirection that is substantially perpendicular to the longitudinal axisof the screw).

The two threaded regions are connected by a hollow central bridgeregion. The hollow central bridge region can be strained and reversiblyelongated, e.g., up to about 8% where the compression screw is formedfrom Nitinol. The hollow central bridge region may be strained andreversibly elongated prior to implantation by releasing that strainafter implantation of the compression screw across the fracture line.The contracting hollow central bridge region can aid in fracturereduction and provide additional therapeutic compression to the bonefracture to provide superior healing. Furthermore, the contractinghollow central bridge region can be shape set to have a 10° axial bend.The bend can be reversibly straightened prior to implantation (whilealso being reversibly elongated), and by releasing that straighteningand elongation after implantation of the compression screw across thefracture line, the hollow central bridge region can return to its 10°bend to provide a more anatomical healing and can return to itsun-elongated state to aid in fracture reduction and provide additionaltherapeutic compression to the bone fracture.

It should be appreciated that the reversible elongation does not need tobe coupled with the 10° bend. It may be beneficial for the compressionscrews of this disclosure not to undergo reversible elongation, andinstead only return to a state with an axial bend followingimplantation.

In an exemplary embodiment, a compression screw system includes acompression screw having a shaft, a screw thread formed on the shaft ata distal location, and a bone-engaging feature formed on the shaft at aproximal location. At least a portion of the shaft disposed between thescrew thread and the bone-engaging feature is non-linear but is capableof being bent to a linear state, and is further capable of beingstretched. A holding element is connectable to the compression screw forreleasably holding at least a portion of the shaft in a linear,stretched condition.

In another exemplary embodiment, an apparatus for securing a first bonefragment to a second bone fragment includes a fusion device including acannulated shaft having a first end and a second end, a firstbone-engaging feature formed on the shaft at a first location, and asecond bone-engaging feature formed on the shaft at a second location.The first bone-engaging feature includes a thread such that the firstend of the shaft may be advanced into a hole in the first bone fragment.The second bone-engaging feature includes at least one barb which, inits unbiased condition, is largely co-radial with the longitudinal axisof the shaft and is capable of being elastically deformed so that thebarbs occupy the region of the cannulation of the shaft such that thesecond end of the shaft may be advanced into a hole in the second bonefragment. The second end is prevented from being withdrawn from the holein the second bone fragment when the at least one barb is in itsunbiased condition.

In yet another exemplary embodiment, a fusion device includes acannulated shaft having a first end and a second end, a firstbone-engaging feature formed on the shaft at a first location, and asecond bone-engaging feature formed on the shaft at a second location.The cannulated shaft can be elongated and constrained in a second state,and upon releasing the constraint, the shaft returns to its un-elongatedstate. The first bone-engaging feature includes a thread such that thefirst end of the shaft may be advanced into a hole in the first bonefragment. The second bone-engaging feature includes at least one barbwhich, in its unbiased condition, is largely co-radial with thelongitudinal axis of the shaft and is capable of being elasticallydeformed so that the barbs occupy the region of the cannulation of theshaft. The second end of the shaft may be advanced into a hole in thesecond bone fragment and is prevented from being withdrawn from the holein the second bone fragment when the at least one barb is in itsunbiased condition.

In yet another exemplary embodiment, an apparatus for securing a firstbone fragment to a second bone fragment includes a fusion device havinga cannulated shaft having a first end and a second end, a firstbone-engaging feature formed on the shaft at a first location, and asecond bone-engaging feature formed on the shaft at a second location.The first bone-engaging feature includes a thread such that the firstend of the shaft may be advanced into a hole in the first bone fragment.The second bone-engaging feature formed includes a pair of planar barbsthat, in their unbiased condition, extend radially from the longitudinalaxis of the shaft and are capable of being elastically deformed so thatthe barbs collapse so as to be largely parallel with the longitudinalaxis of the shaft. The second end of the shaft may be advanced into ahole in the second bone fragment and is prevented from being withdrawnfrom the hole in the second bone fragment when the pair of barbs is inits unbiased condition.

In yet another exemplary embodiment, an apparatus for securing a firstbone fragment to a second bone fragment includes a fusion device. Thedevice includes a cannulated shaft having a first end and a second end.The cannulated shaft can be elongated and constrained in a second state,and upon releasing the constraint, the shaft returns to its un-elongatedstate. A first bone-engaging feature is formed on the shaft at a firstlocation and a second bone-engaging feature is formed on the shaft at asecond location. The first bone-engaging feature includes a thread suchthat the first end of the shaft may be advanced into a hole in the firstbone fragment. The second bone-engaging feature includes a pair ofplanar barbs that, in their unbiased condition, extend radially from thelongitudinal axis of the shaft and are capable of being elasticallydeformed so that the barbs collapse so as to be largely parallel withthe longitudinal axis of the shaft. The second end of the shaft may beadvanced into a hole in the second bone fragment and is prevented frombeing withdrawn from the hole in the second bone fragment when the pairof barbs is in its unbiased condition.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of this disclosure will becomeapparent to those skilled in the art from the following detaileddescription. The drawings that accompany the detailed description can bebriefly described as follows.

FIGS. 1, 2, 3, and 4 schematically illustrate a compression screw systemaccording to an exemplary aspect of this disclosure.

FIGS. 5 and 6 schematically illustrate internal retaining pointsdisposed within the interior of a strained (i.e., stretched) andstraightened (i.e., un-bent) compression screw.

FIGS. 7, 8, and 9 schematically illustrate an intramedullary fusiondevice according to an exemplary aspect of this disclosure.

FIGS. 10 and 11 schematically illustrate an intramedullary fusion deviceloaded onto a delivery device.

FIGS. 12, 13, and 14 schematically illustrate another exemplaryintramedullary fusion device.

FIGS. 15 and 16 schematically illustrate another intramedullary fusiondevice loaded onto a delivery device.

DETAILED DESCRIPTION

This disclosure describes the use of novel intramedullary devices thatare better able to bring bone fragments into close proximity with eachother, generate a compressive load, and maintain that compressive loadfor a prolonged period of time while healing occurs.

A compression screw system according to an exemplary aspect of thisdisclosure includes, inter alia, a compression screw and an internalretaining pin. The compression screw is made of a shape memory materialsuch that a portion of a shaft of the compression screw is positionablein a bent condition. The internal retaining pin is insertable into thecompression screw and is configured for moving the portion from the bentcondition to a straightened and stretched condition.

In a further embodiment, an internal retaining pin holds a portion of ashaft in a straightened and stretched condition while a compressionscrew is inserted into a bone, and the internal retaining pin isconfigured for releasing the portion from the stretched and straightenedcondition back toward a bent condition after the compression screw hasbeen inserted into the bone.

In a further embodiment, a shape memory material is Nitinol.

In a further embodiment, a shape memory material is PEEK.

In a further embodiment, a compression screw includes a central lumen,and an internal retaining pin extends into the central lumen.

In a further embodiment, an internal retaining pin is seated against anannular shoulder of a central lumen when a portion of a shaft is in astraightened and stretched condition.

In a further embodiment, a first screw thread is formed on a shaft at adistal location and a second screw thread is formed on the shaft at aproximal location, and a portion of the shaft is disposed between thefirst and second screw threads.

In a further embodiment, a first screw thread and a second screw threadinclude different thread pitches.

In a further embodiment, a portion of a compression screw is bent at anangle of about 10° relative to a longitudinal axis of the compressionscrew when in a bent condition.

In a further embodiment, a first drive feature is provided on acompression screw and a second drive feature is provided on an internalretaining pin, and the first drive feature and the second drive featureare engageable to insert the compression screw into bone.

An intramedullary fusion device according to an exemplary aspect of thisdisclosure includes, inter alia, a shaft made of a shape memory materialand including a threaded end region, a barbed end region, and a centralbridge region between the threaded end region and the barbed end region.A first bone-engaging feature is provided on the threaded end region,and a second bone-engaging feature is provided on the barbed end region.The second bone-engaging feature is movable between an unbiasedcondition in which it is co-radial with a longitudinal axis of the shaftand a biased condition in which a cross-sectional profile of the barbedend region is reduced.

In a further embodiment, a shape memory material is Nitinol.

In a further embodiment, a shape memory material is PEEK.

In a further embodiment, a first bone-engaging feature includes a threadhelically wrapped around a shaft at a threaded end region.

In a further embodiment, a second bone-engaging feature includes a pairof planar barbs.

In a further embodiment, a pair of planar barbs are generally parallelto the longitudinal axis of the shaft when positioned in the biasedcondition.

In a further embodiment, a second bone-engaging feature occupies atleast a portion of a cannulation that extends through a shaft when asecond bone-engaging feature is positioned in a biased condition.

In a further embodiment, a central bridge region is neither threaded norbarbed.

In a further embodiment, an intramedullary fusion device is receivablewithin a recess of a delivery device.

In a further embodiment, a second bone-engaging feature is removablyheld within a recess of a delivery device.

FIGS. 1-4 illustrate a compression screw 5 for bringing bone fragmentsinto close proximity with each other, generating a compressive load, andmaintaining that compressive load for a prolonged period of time whilethe bone tissue heals. The compression screw 5 is manufactured from ashape memory material (e.g., a material capable of exhibitingsuperelasticity and/or a temperature induced shape change). The shapememory material may be a metal alloy (e.g., Nitinol) or a polymer (e.g.,appropriately processed PEEK). The compression screw 5 is designed toengage bone fragments and generate compression between the bonefragments.

The compression screw 5 includes a proximal threaded region 105 having aproximal screw thread 110 and a distal threaded region 115 having adistal screw thread 120. The thread pitch of proximal screw thread 110is finer than the thread pitch of distal screw thread 120 (i.e., thethread pitch on proximal threaded region 105 has more threads per inchthan the thread pitch on distal threaded region 115). This pitchdifferential reduces fractures and generates compression. The respectivethread geometry on the proximal threaded region 105 and the distalthreaded region 115 are mirrored, thus creating a “book-end” effect thatincreases the compression holding capabilities of the compression screw5 when it extends across a fracture line in bone (e.g., the threadgeometry on the proximal threaded region 105 has an incline in theproximal direction and a flat surface in the distal direction that issubstantially perpendicular to the longitudinal axis of the screw, andthe thread geometry on the distal threaded region 115 is mirrored,having an incline in the distal direction and a flat surface in theproximal direction that is substantially perpendicular to thelongitudinal axis of the screw).

The proximal threaded region 105 and the distal threaded region 115 areconnected by a hollow central bridge region 125. The hollow centralbridge region 125 can be strained and reversibly elongated because thecompression screw 5 is manufactured from a shape memory material. In anembodiment, the compression screw 5 is formed out of Nitinol, and thehollow central bridge region 125 can be strained and reversiblyelongated by up to 8% without taking a set. By straining and reversiblyelongating the hollow central bridge region 125 prior to implantationacross a bone fracture line, and by thereafter releasing that strainafter implantation across the fracture line, the hollow central bridgeregion 125 can provide additional compression to the bone fracture.

The compression screw 5 includes a drive feature 130 (e.g., a hexagonalboss) at the proximal threaded region 105 for engagement by anappropriate driver (not shown) for turning the compression screw 5(e.g., into bone). Additionally, the distal threaded region 115 of thecompression screw 5 may include self-drilling features (e.g., cuttingedges) and self-tapping features (e.g., flutes), although notspecifically shown in the figures.

The compression screw 5 also includes a central lumen 145 (see FIG. 4)which extends the length of the proximal threaded region 105 and thecentral bridge region 125. The central lumen 145 generally includes adistal bore 150 and a proximal counterbore 160. The distal bore 150terminates at an annular shoulder 165 that may lie in a planeperpendicular to the longitudinal axis of the compression screw 5. Theproximal counterbore 160 has a diameter which is wider than the diameterof the distal bore 150. The proximal counterbore 160 is threaded, e.g.,with an internal thread 175 (for purposes of clarity, not shown).

In the un-constrained state, the central bridge region 125 may be bentalong its central axis. In an embodiment, such as shown in FIG. 2, thehollow central bridge region 125 may be bent at an angle Θ (e.g., up toabout 10°) relative to the central axis.

FIGS. 5-6 illustrate a compression screw system 100. The compressionscrew system 100 generally includes a compression screw 5 and aninternal retaining pin 200. In an embodiment, the compression screw 5and the internal retaining pin 200 are provided as part of a sterilizedkit. The kit may include additional instruments to aid in theimplantation of the compression screw 5 (e.g., k-wire, drill bit, screwsize guide, etc.).

The internal retaining pin 200 is selectively inserted into thecompression screw 5. The internal retaining pin 200 is sized so thatwhen the compression screw 5 is strained (i.e., stretched) and un-bent(i.e., straightened), the internal retaining pin 200 is fully seatedagainst the annular shoulder 165 of the distal bore 150 of the centrallumen 145 (see FIG. 6).

The internal retaining pin 200 is capable of maintaining the compressionscrew 5 strained and straightened. The compression screw system 100 isimplanted by driving the compression screw 5 using a drive feature 210of the internal retaining pin 200 and the drive feature 130 of thecompression screw 5. Upon implantation, removal of the internalretaining pin 200 causes the compression screw 5 to attempt to shortento its original length and also bend to its bent state.

FIGS. 7-9 illustrate an intramedullary fusion device 305 manufacturedfrom a shape memory material. The shape memory material may be a metalalloy (e.g., Nitinol) or a polymer (e.g., appropriately processed PEEK).The intramedullary fusion device 305 includes a threaded end region 310,a barbed end region 315, and a central bridge region 320 connecting thethreaded end region 310 to the barbed end region 315. The intramedullaryfusion device 305 may be cannulated (see bore or cannulation 311 of FIG.9) to allow the intramedullary fusion device 305 to be installed over ak-wire if desired, while also allowing a k-wire to be passed through theintramedullary fusion device 305 following implantation if the surgeondesires to fuse a distal or proximal joint. The barbed end region 315can be reversibly deformed into the cannulation 311 during insertion,and then attempt to return to the un-deformed state following insertion,thereby providing excellent torsional stability at the fusion site.

The threaded end region 310 includes a thread 325 which may be helicallywound around the longitudinal axis of the intramedullary fusion device305. The threaded end region 310 engages the intramedullary canal anddistributes pressure across the intramedullary canal post-implantation.

The barbed end region 315 includes a plurality of barbs 335 which, intheir unbiased condition, are co-radial with the longitudinal axis ofthe intramedullary fusion device 305. During implantation, the barbs 335can be deformed to a position in which they occupy the region of thecannulation 311 so as to reduce the cross-sectional profile of thebarbed end region 315. This simplifies insertion into a drilled hole inbone, for example. The barbs 335 can be deformed during implantation insuch a way that they partially occupy the cannulation 311 of theintramedullary fusion device 305 (i.e., where barbs 335 are deformed toa point past parallel to the longitudinal axis of intramedullary fusiondevice 305), thereby further reducing the cross-sectional area of thebarbed end region 315. This is beneficial for accessing theintramedullary canal through a small drilled hole, for example.

While FIG. 7 illustrates a device with four barbs 335 on the barbed endregion 315, it should be appreciated that barbed end region 315 couldinclude more or fewer barbs. Upon the barbed end region 315 beingpressed into a drilled hole, the barbs 335 attempt to return to beingco-radial with the body of the intramedullary implant, thus exerting anexpansive force on the intramedullary canal.

The central bridge region 320 may include a generally cylindrical shapeand may be sized to include an outer diameter that is smaller than themajor diameters of the threaded end region 310 and the barbed end region315.

FIGS. 10-11 depict a delivery device 400 for implanting theintramedullary fusion device 305 of FIGS. 7-9. The delivery device 400includes a handle 410 and an intramedullary engagement region 420. Theintramedullary engagement region 420 has one or more drive features 430that can be positioned between the barbs 335 of the intramedullaryfusion device 305. This allows the intramedullary fusion device 305 tobe placed in the delivery device 400 and then be screwed into bone. Inan embodiment, the intramedullary fusion device 305 is implantedaccording to the following exemplary method:

1. Perform incisions and bone resections and address soft tissuecontractures as necessary. Note: Resections should be perpendicular tothe long axis of the bones in the transverse plane. In the sagittalplane, resections should be perpendicular to the long plane.

2. Determine the correct implant size by using a sizing guide.

3. Open the chosen implant kit.

4. Insert a trocar tip of a guide wire into the proximal phalanx alongits central axis.

Advance the wire until it pierces the proximal cortex of the proximalphalanx.

5. Place the provided drill bit over the guide wire and drill theproximal phalanx until the boss of the bit meets the cut surface.

6. Remove the drill bit and guide wire.

7. Insert the trocar tip of the guide wire into the middle phalanx alongits central axis. Continue to drive the guide wire distally through bothmiddle and distal phalanges until it exists the toe. Continue to drivethe guide wire distally until the laser etched line on guide wirecontacts the cut surface of the middle phalanx.

8. Using the implant pre-loaded on the delivery device, place theimplant/delivery device over the guide wire and drive the threadedportion of the implant into the middle phalanx by screwing it in place.Continue to drive the threaded portion until the rim of the driver iscompletely flush with the cut surface.

9. Remove and dispose of the driver socket from the implant leaving thebarbed portion exposed.

10. Position the implant in line with the proximal phalanx. Insert thebarbed portion of the implant into the pre-drilled hole in the proximalphalanx. Apply axial force until the implant is completely buried andthe opposing faces of the middle and proximal phalanges come intocontact. Optional: If temporary guide wire fixation of the MTP joint isdesired, drive the exposed tip of the guide wire through the implant andback into the metatarsal to stabilize the MTP joint.

11. Close the surgical site according to surgical preference. If theguide wire is temporarily left in place, trim with wire cutters.

12. Repeat steps 1-9 for each additional implant used.

FIGS. 12-14 illustrate another exemplary intramedullary fusion device505 manufactured from a shape memory material. The shape memory materialmay be a metal alloy (e.g., Nitinol) or a polymer (e.g., appropriatelyprocessed PEEK). The intramedullary fusion device 505 includes athreaded end region 510, a barbed end region 515, and a central bridgeregion 520 connecting between the threaded end region 510 and the barbedend region 515. The intramedullary fusion device 505 may be cannulated(see bore or cannulation 511 of FIG. 14) to allow the intramedullaryfusion device 505 to be installed over a k-wire, or to allow a k-wire tobe passed through the intramedullary fusion device 505 followingimplantation if the surgeon desires to fuse a distal or proximal joint.The barbed end region 515 can reversibly deform such that the barbs aregenerally parallel to the longitudinal axis of the intramedullary fusiondevice 505 during insertion, and then attempt to return to theun-deformed state following implantation, thereby providing excellenttorsional stability at the fusion site.

The threaded end region 510 includes a thread 525 which is helicallywound around the longitudinal axis of the intramedullary fusion device505. The thread 525 may be self-cutting and/or self-tapping to aid inimplantation.

The barbed end region 515 includes a pair of planar barbs 535 which, intheir unbiased condition, extend radially from the longitudinal axis ofthe intramedullary fusion device 505. During implantation, the barbs 535can be deformed to a position such that they are substantially parallelto the longitudinal axis of the intramedullary fusion device 505 so asto reduce the cross-sectional profile of the barbed end region 515, andthus allowing for insertion into a drilled hole in bone, for example.This is beneficial for accessing the intramedullary canal through asmall prepared hole.

While FIG. 12 illustrates a device with a single pair of planar barbs535 on the barbed end region 515, it should be appreciated that barbedend region 515 can be made with more than one pair of barbs. Upon barbedend region 515 being pressed into a prepared hole, barbs 535 attempt toreturn to their unbiased configuration and exert an expansive force onthe intramedullary canal.

The central bridge region 520 may include a generally cylindrical shapeand may be sized to include an outer diameter that is smaller than themajor diameters of the threaded end region 510 and the barbed end region515.

FIGS. 15-16 depict a delivery device 600 for implanting theintramedullary fusion device 505 described above with reference to FIGS.12-14. The delivery device 600 includes a handle 610 and anintramedullary engagement region 620. The intramedullary engagementregion 620 has a recess 619 (see FIG. 16) to accept and hold theintramedullary fusion device 505. This allows the intramedullary fusiondevice 505 to be placed in the delivery device 600 and then be screwedinto the bone. In an embodiment, the intramedullary fusion device 505 isimplanted according to the following exemplary method:

1. Perform incisions and bone resections and address soft tissuecontractures as necessary. Note: Resections should be perpendicular tothe long axis of the bones in the transverse plane. In the sagittalplane, resections should be perpendicular to the long plane.

2. Determine the correct implant size by using a sizing guide.

3. Open the chosen implant kit.

4. Insert a trocar tip of the k-wire into the proximal phalanx along itscentral axis. Advance the wire until it pierces the proximal cortex ofthe proximal phalanx.

5. Place the provided drill bit over the guide wire and drill theproximal phalanx until the boss of the bit meets the cut surface.

6. Remove the drill bit and guide wire.

7. Using a supplied broach, broach the drilled hole.

8. Insert a trocar tip of the guide wire into the middle phalanx alongits central axis. Continue to drive the guide wire distally through bothmiddle and distal phalanges until it exists the toe. Continue to drivethe guide wire distally until the laser etched line on guide wirecontacts the cut surface of the middle phalanx.

9. Using the implant pre-loaded on the delivery device, place theimplant/delivery device over the guide wire and drive the threadedportion of the implant into the middle phalanx by screwing it in place.Continue to drive the threaded portion until the rim of the driver iscompletely flush with the cut surface and the implantation drivermarking is pointed up.

10. Remove and dispose of the driver socket from the implant leaving thebarbed portion exposed.

11. Position the implant in line with the proximal phalanx. Insert thebarbed portion of the implant into the prepared hole in the proximalphalanx. Apply axial force until the implant is completely buried andthe opposing faces of the middle and proximal phalanges come intocontact. Optional: if temporary guide wire fixation of the MTP joint isdesired, drive the exposed tip of the guide wire through the implant andback into the metatarsal to stabilize the MTP joint.

12. Close the surgical site according to surgical preference. If theguide wire is temporarily left in place, trim with wire cutters.

13. Repeat steps 1-9 for each additional implant used.

The foregoing description shall be interpreted as illustrative and notin any limiting sense. A worker of ordinary skill in the art wouldrecognize that certain modifications could come within the scope of thisdisclosure. For these reasons, the following claims should be studied todetermine the true scope and content of this disclosure.

What is claimed is:
 1. A method for applying compression within a body,the method comprising: drilling a hole across a bone fracture line of apatient, wherein the bone fracture line separates a first bone fragmentfrom a second bone fragment; positioning a k-wire through the hole;positioning the k-wire through a through-hole of a compression implantsuch that the compression implant is positioned at least partiallythrough the hole, wherein the compression implant includes a shafthaving a threaded first end and a second end opposite the threaded firstend, wherein the shaft further includes a Nitinol expandable sectionpositioned between the threaded first end and the second end, andwherein the through-hole of the compression implant extends from thethreaded first end of the shaft to the second end of the shaft; securingthe threaded first end of the shaft of the compression implant to thesecond bone fragment; and transitioning the Nitinol expandable sectionof the shaft from a first length to a second length, wherein the Nitinolexpandable section is biased to the first length due to the shape memoryproperties of the Nitinol material to thereby provide a compressiveforce across the bone fracture line of the patient.
 2. A method forapplying compression within a body, the method comprising: drilling ahole across a bone fracture line of a patient, wherein the bone fractureline separates a first bone fragment from a second bone fragment;positioning a compression implant at least partially through the hole,wherein the compression implant includes a shaft having a threaded firstend and a second end opposite the threaded first end, and wherein theshaft further includes a Nitinol expandable section positioned betweenthe threaded first end and the second end; securing the threaded firstend of the shaft of the compression implant to the second bone fragment;transitioning the Nitinol expandable section of the shaft from a firstlength to a second length, wherein the Nitinol expandable section isbiased to the first length due to the shape memory properties of theNitinol material to thereby provide a compressive force across the bonefracture line of the patient; positioning a k-wire through athrough-hole of the compression implant after securing the threadedfirst end of the shaft of the compression implant to the second bonefragment, wherein the through-hole of the compression implant extendsfrom the threaded first end of the shaft to the second end of the shaft;and fusing a joint distal to the bone fracture line and/or a jointproximal to the bone fracture line.
 3. A method for applying compressionwithin a body, the method comprising: drilling a hole across a bonefracture line of a patient, wherein the bone fracture line separates afirst bone fragment from a second bone fragment; positioning acompression implant at least partially through the hole, wherein thecompression implant includes a shaft having a threaded first end and asecond end opposite the threaded first end, and wherein the shaftfurther includes a Nitinol expandable section positioned between thethreaded first end and the second end; securing the threaded first endof the shaft of the compression implant to the second bone fragment; andtransitioning the Nitinol expandable section of the shaft from a firstlength to a second length, wherein the Nitinol expandable section isbiased to the first length due to the shape memory properties of theNitinol material to thereby provide a compressive force across the bonefracture line of the patient.
 4. The method of claim 3, wherein theexpandable section transitions from the first length to the secondlength when a driver turns the compression implant.
 5. The method ofclaim 3, further comprising: positioning a k-wire through the hole; andpositioning the k-wire through a through-hole of the compression implantprior to securing the threaded first end of the shaft of the compressionimplant to the second bone fragment, wherein the through-hole of thecompression implant extends from the threaded first end of the shaft tothe second end of the shaft.
 6. The method of claim 3, furthercomprising: positioning a k-wire through a through-hole of thecompression implant after securing the threaded first end of the shaftof the compression implant to the second bone fragment, wherein thethrough-hole of the compression implant extends from the threaded firstend of the shaft to the second end of the shaft; and fusing a jointdistal to the bone fracture line.
 7. The method of claim 3, furthercomprising: positioning a k-wire through a through-hole of thecompression implant after securing the threaded first end of the shaftof the compression implant to the second bone fragment, wherein thethrough-hole of the compression implant extends from the threaded firstend of the shaft to the second end of the shaft; and fusing a jointproximal to the bone fracture line.
 8. The method of claim 3, whereinthe first end of the shaft comprises a self-drilling feature, andwherein the first end of the shaft comprises a self-tapping feature. 9.The method of claim 8, wherein the self-drilling feature comprises oneor more cutting edges.
 10. The method of claim 8, wherein theself-tapping feature comprises a flute.
 11. The method of claim 3,wherein the second length of the expandable section of the shaft is upto 8% greater than the first length of the expandable section of theshaft.